This invention relates generally to the field of power generation and more specifically to a component for a gas turbine engine, and in particular to a component formed of a single crystal superalloy material.
Gas turbine engines include a compressor section for supplying a flow of compressed combustion air, a combustor section for burning a fuel in the compressed combustion air, and a turbine section for extracting thermal energy from the combustion air and converting that energy into mechanical energy in the form of a shaft rotation. Many parts of the combustor section and turbine section are exposed directly to the hot combustion gasses; for example the combustor, the transition duct between the combustor and the turbine section, and the turbine stationary vanes, rotating blades and surrounding ring segments.
It is also known that increasing the firing temperature of the combustion gas may increase the power and efficiency of a combustion turbine. Modern high efficiency combustion turbines have firing temperatures that may be well in excess of the safe operating temperature of the structural materials used to fabricate the hot gas flow path components. Special superalloy materials have been developed for use in such high temperature environments, and these materials have been used with specific cooling arrangements, including film cooling, backside cooling and insulation. Superalloys are well known in the art. They are based on Group VIIIB elements and usually consist of various combinations of Fe, Ni, Co, and Cr, as well as lesser amounts of W, Mo, Ta, Nb, Ti, and Al. The three major classes of superalloys are nickel-based, iron-based, and cobalt-based alloys. Nickel-based superalloys can be either solid solution or precipitation strengthened. Solid solution strengthened alloys are used in applications requiring only modest strength. A precipitation-strengthened alloy is required in the most demanding applications such as the hot combustion gas flow path sections of gas turbine engines. The primary strengthening phase in nickel-based superalloys is Ni3(Al, Ti) and is termed gamma prime. A characteristic of the gamma prime strengthened nickel-based superalloys is that they retain their strength at elevated temperatures and may be used in load-bearing structures to the highest homologous temperature of any common alloy system (Tm=0.9, or 90% of their melting point).
Airfoil members such as blades and vanes formed of superalloy materials may be cast as monolithic structures with internal cooling channels being defined during the casting process by ceramic inserts. The inserts are later dissolved to create the open cooling channels within the cast component.
Single crystal superalloys offer improved mechanical properties and high temperature capabilities compared with conventionally cast components. However, it is very difficult to cast a large single crystal component without developing an unacceptable level of spurious grains and/or excessively large low angle boundaries. First-generation superalloys such as PWA 1483 contain no rhenium and are generally difficult to cast as a single crystal. Second-generation superalloys containing about 3 wt. % rhenium, for example PWA 1484 and CMSX-4, have been developed to obtain improved creep properties. The second generation superalloys are generally more difficult to cast than first-generation superalloys. Casting yields for large complex single crystal second generation superalloy turbine blades and vanes containing internal cooling passages may be no more than about 5-20%, making the use of such materials prohibitively expensive in many applications. Third-generation superalloys containing more than 3% and up to about 6% rhenium (for example CMSX-10) may be even more difficult to cast as complex single crystal turbine components.
One approach that has been used to facilitate the fabrication of complex single crystal shapes is described in U.S. Pat. No. 6,331,217. This approach involves casting a plurality of relatively simple single crystal sub-components, then joining the sub-components together with a transient liquid phase bonding process. The strength of the component at the bond location may be somewhat lower than the strength in pure single crystal castings, so the bond location is selected to be in an area of low stress. This approach has resulted in improved component yields; however, further improvements in fabrication techniques are desired.
U.S. Pat. No. 6,190,133 describes an airfoil component for the compressor section of a gas turbine engine. The airfoil component is formed of a equiaxed titanium alloy outer shell that is stiffened with an inner core member. The core member has a modulus of elasticity that is greater than that of the outer shell and may be titanium aluminide. The core member may be fabricated by a combination of machining, forging, casting and powder metallurgy techniques. The pre-formed core member is placed into an airfoil shaped mold and the outer shell is cast around the core member. The airfoil component and method of fabrication described in the ""133 patent are used in the relatively cool compressor section of a gas turbine. Such components and methods of fabrication are not useful for gas turbine components that are exposed to the hot combustion gasses where temperatures may reach 1,600xc2x0 C. or more.
Accordingly, an improved component and an improved method of manufacturing the component are needed for high temperature applications such as the hot combustion gas flow path of a gas turbine engine.
A hybrid blade for the hot gas pathway portion of a gas turbine engine is described herein as including: a cast single crystal superalloy portion comprising an outer surface defining an airfoil and an inner surface defining a cavity; and a superalloy powder metallurgy material portion comprising a core disposed within the cavity and a root extending beyond the cavity, the superalloy powder metallurgy material portion being metallurgically bonded to the cast single crystal superalloy portion along the inner surface. The hybrid blade may further include a cooling passage formed through the superalloy powder metallurgy material portion.
A hybrid component is described herein as including: a first portion comprising a cast single crystal material; and a second portion comprising a powder metallurgy material. The second portion may be a relatively complex shape compared to the first portion. The second portion may be subjected to a lower level of stress than the first portion during use of the component. The first portion may be a cast single crystal superalloy material, and there may be a metallurgical bond between the first portion and the second portion. The first portion may be a cast single crystal superalloy material comprising at least 3 wt. % rhenium.
A method of fabricating a hybrid component is described herein as including the steps of: forming a first portion comprising a cast single crystal material; and forming a second portion comprising a powder metallurgy material. The method may include: casting the first portion to comprise an airfoil having a hollow center; and using the airfoil as a mold for at least partially containing powder during the step of forming a second portion. A melting point suppressant material may be applied to a bond surface of the first portion to facilitate the formation of a metallurgical bond between the first portion and the second portion along the bond surface. The method may further include forming the first portion to be an airfoil section and forming the second portion to be a root section attached to the airfoil section.